Over the course of human history, on-site wastewater treatment systems have evolved from pit privies to installations capable of producing a disinfected effluent fit for human consumption. Modern conventional on-site wastewater treatment systems consist primarily of a septic tank and a soil absorption field, also known as a subsurface wastewater infiltration system.
It has been estimated that in 2007, about 20% of U.S. households (i.e., about 26.1 million houses), utilized on-site septic systems, a majority of which were installed decades ago and have long since passed their recommended replacement dates.
The primary pollutants released from on-site septic systems are nitrogen (N), phosphorus (P), and disease-causing pathogens. Of these, problems associated with P pollution have been recognized as an increasing worldwide concern due to the role of P in accelerating eutrophication. Consequently, governmental agencies across the world have established or are in the process of establishing regulations for wastewater discharges originating from point sources, such as municipal treatment plants, industry discharges from factories, houses, housing developments, etc., as the most expedient means of reducing P pollution. The increasingly stringent regulations increase the cost of treating wastewater from point pollution sources, and motivate the need for new technologies to provide efficient P removal from wastewater generated by such sources.
Existing technologies for P removal from wastewater generated by point pollution sources suffer from three major shortcomings. The first is that they cannot achieve the high level of P filtration required by present and anticipated regulations (e.g., 1 mg/L presently and perhaps as low as 0.03 mg/L in the near future). The second is that a few emerging technologies generate a highly alkaline filtered effluent, which is known to be detrimental to the environment, and in particular to fish and other aquatic life. The third major shortcoming is that they are energy intensive and require a high level of maintenance.